Suspected Abu Sayyaf militants kidnapped three Indonesian fishermen on the weekend in the latest in a series of incidents highlighting weak security in the Cerebes Sea that borders Malaysia, Indonesia and the Philippines.

The head of Indonesia's intelligence agency said Monday that the men were working on a Malaysian fishing boat off Lahad Datu in the Malaysian part of northern Borneo. Sutiyoso, who goes by one name, said the kidnappers fled with their hostages into Philippine waters.

Several crew on the fishing boat escaped and are now in Malaysia.

Indonesia, Malaysia and the Philippines agreed in May to carry out coordinated patrols in border waters following kidnappings of Indonesian tug boat and barge crews by Abu Sayyaf militants based in the southern Philippines. The three governments are concerned that unchecked kidnappings, piracy and other crime could undermine commerce in the region.

The Indonesians, who were held captive in the jungles of Sulu province in the southern Philippines, were later released. The Indonesian government denied it had been involved in paying a ransom.

“We are still investigating this case and continue to coordinate with the related institutions in the Philippines to find the location where the three hostages are being held,” Sutiyoso told The Associated Press. “We suspect that the hostages are held by a militant group which is part of the Abu Sayyaf network.”

The Philippines, meanwhile, has stepped up its military offensive against Abu Sayyaf, which earlier this year beheaded two Canadians it had held hostage since September.